# DOMDocument::getElementById

(PHP 5, PHP 7, PHP 8)

DOMDocument::getElementById — Searches for an element with a certain id

### Beschreibung

public DOMDocument::getElementById(string `$elementId`): ?DOMElement

This function is similar to DOMDocument::getElementsByTagName but searches for an element with a given id.

For this function to work, you will need either to set some ID attributes with DOMElement::setIdAttribute or a DTD which defines an attribute to be of type ID. In the later case, you will need to validate your document with DOMDocument::validate or DOMDocument::$validateOnParse before using this function.

### Parameter-Liste

`elementId`

  The unique id value for an element.

### Rückgabewerte

Returns the DOMElement or `null` if the element is not found.

### Beispiele

Beispiel #1 DOMDocument::getElementById() Example

Die folgenden Beispiele verwenden book.xml mit dem folgenden Inhalt:

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE books [
      <!ELEMENT books   (book+)>
      <!ELEMENT book    (title, author+, xhtml:blurb?)>
      <!ELEMENT title   (#PCDATA)>
      <!ELEMENT blurb   (#PCDATA)>
      <!ELEMENT author  (#PCDATA)>
      <!ATTLIST books   xmlns        CDATA  #IMPLIED>
      <!ATTLIST books   xmlns:xhtml  CDATA  #IMPLIED>
      <!ATTLIST book    id           ID     #IMPLIED>
      <!ATTLIST author  email        CDATA  #IMPLIED>
    ]>
    <?xml-stylesheet type="text/xsl" href="style.xsl"?>
    <books xmlns="http://books.php/" xmlns:xhtml="http://www.w3.org/1999/xhtml">
      <book id="php-basics">
        <title>PHP Basics</title>
        <author email="jim.smith@basics.php">Jim Smith</author>
        <author email="jane.smith@basics.php">Jane Smith</author>
        <xhtml:blurb><![CDATA[
    <p><em>PHP Basics</em> provides an introduction to PHP.</p>
    ]]></xhtml:blurb>
      </book>
      <book id="php-advanced">
        <title>PHP Advanced Programming</title>
        <author email="jon.doe@advanced.php">Jon Doe</author>
      </book>
    </books>

`<?php
$doc = new DomDocument;
// We need to validate our document before referring to the id
$doc->validateOnParse = true;
$doc->load('examples/book.xml');
echo "The element whose id is 'php-basics' is: " . $doc->getElementById('php-basics')->tagName . "\n";
?>`

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

    The element whose id is 'php-basics' is: book

### Siehe auch

- DOMDocument::getElementsByTagName() - Searches for all elements with given local tag name

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